Transducers are devices that covert one type of energy into another. Acoustic transducers in particular convert electrical signal to acoustic signals (sound waves) in a transmit mode (e.g., a speaker application), and/or convert received acoustic waves to electrical signals in a receive mode (e.g., a microphone application). Similarly, optical transducers convert electrical signal to optical signals (light) in a transmit mode (e.g., a light source application), and/or convert received optical signals to electrical signals in a receive mode (e.g., a light sensor application).
Dual sensing applications require both acoustic and optical sensing using both acoustic and optical transducers. For example, a paper/document feeder typically includes an acoustic sensing system that determines thicknesses of paper to avoid jamming, and an optical sensing system that detects edges of paper. In this case, two separate sets of transducers are required. A set of acoustic transducers includes transmitting acoustic transducers that send ultrasonic signals and sensing acoustic transducers that receive those ultrasonic signals, e.g., for determining paper thickness. Similarly, a set of optical transducers includes transmitting optical transducers, such as light emitting diodes (LEDs) or laser diodes, that send optical signals and sensing optical transducers, such as photodiodes, that receive the transmitted optical signals, e.g., for determining paper edges. The implementation of multiple transducer systems requires additional space and is generally inefficient.